wildhaber



Dec. 4, 1928. 1,693,687

E. WILDHABER METHOD OF PRODUCING GEARS Filed Dec. 30, 1924 4 Sheets-Sheet 1 ,1 x mmvrom zmesa Wildiuzer E. WILDHABER METHOD OF PRODUCING GEARS Dec. 4, 1928.

Filed Dec.'30, 1924 4 Sheets-Sheet 2 Dec. 4, 1928. 1,693,687

E. WILDHABER METHOD OF rnonucme emns Filed Dec. 50, 1924 I 4 Sheets-Sheet 3 11y VEN TOR.

.' 4115A T0RNEY Dec. 4, 1928. 1,693,687

E. WILDHABER METHOD OF PRODUCING GEARS Filed Dec. 30, 1924 4 sheets sheec 4 Patented Dec. 4, 1928.

UNITED STATES ERNEST WILDHABER, or ROCHESTER, new YORK, ASSIGNOR T GLEASON worms, on

RocHns'rE-nnnw YoRK, A ooRronArIcN or new YoRK.

METHOD or ZEROIDUGING GEARS.

Application filed December 30, 1924. Serial No. 758,861.

This invention relates to methods of producing gears, one Object of the invention being to provide an eflicient method for hobbing curved tooth tapered gears having the speed,

economy and other advantages characteristic of hobbing processes. A further object is to provide an advantageous method of this nature adapted for cutting curved tooth tapered gears of a variety characterizedby pitch line curvature and spiral angle of the ClQSIIGdmoderate proportions. i To these and other ends the invention resides in certain improvements and'coinbinations of parts, all as will be hereinafter more fully described, the novel features being pointed out in the claims at the end of the specification. l i In the drawings Figure 1 is a plan view showing the pitch surfaces of a hob and gear arranged in cutting relation in accordance with the invention, the gear being shown in development, or in other words, as a crown gear;

Figure 2 is an elevation of the same; Figure 8 shows the'pitch plane of the developed or crown gear and the pitch cone of the hub in development; I

Figure 4c shows in development the preferred form of hob thread at the pitch line and meshing with the developed pitch surface of the gear to be cut or the pitch surface of the corresponding crown gear, the shaded por- 'tions representing sections through the teeth; Figures 5 and 6 are a plan and elevation, respectively, illustrating the generation of a beveled pinion; 1

Figures 7 andS are a plan and elevation illustrating the methodof generating a gear adapted to mate with the pinion of-Figures 5and6; I

Figure 91 shows a development of the. pitch cone of a hob for carrying out the present invention;

Figures 10 and 11 are a plan and elevation, respectively,'ill u strating the means and method of grinding the flutes of the hob Figure 12 is a view of a complete hob for carrying out the present invention, and 7 Figures 13 and 14 are views of a cutting face of the hob and illustrating two difierent methods of relieving the same.

Similar reference numerals throughout the several views indicate the same parts. 7

p The preferred form. of the method in ac eordanee with the present inveutian, is cma'ied out by a hob employed and its cutting edges are formed by gashes extending along lines which are curved both in the actual tool and in development and extending also perpendicularly to the threads. The hob thread will be first described in its general aspects and then with reference more particularly to thepreferred embodiment, thereof. v

The thread of such a hob should preferably be able to mesh with a crown gear having identical pitch lines on the convex and concave sides of the teeth and the thread is preferably. of a form which meshes with the blank to be cut in such 'a way that the pitch lines of the blank are produced by pitch lines of the hob.

ing the development of a gear to be cut. A133 is the axis of a taper hob intersecting'plane2 1,693,687 arser orries .70 Referring more particularly to. Figures'l at a point l which is the apex of the conical pitch surface 5 of the hub. Pitch surfaces 2 and 5 contact with each other in a line 6. At all points along this line 6,the pitch lines 7 of the hub thread match the'pitch lines 8 of the teeth of'the gear, or in other words, the pitch lines 7 and 8 contact in points such as 9, 10, of

line 6, and the latter may be considered as the line of action between the two pitch surfaces. When the hob and gear are turned about their respective axes 3 and I at a fixed ratio, the contact points 9, 10, will travel along the line of action 6. g

In the constructions heretofore employed, a contact point such as 9, 10, travels at a constant rate along'the line of actionG, and theapex of the hob in such case must be located at a point 11 on a perpendicular 12 drawn from the gear center 1 to line 6, asfollows from the relations and equations hereinafter explained. I

It has been found however that sucha line 6 may also be a line of action betweentwo pitch surfaces where the apex'of the hobldoes not lie at 11 on the perpendicular but hasany other position such as 4 outside the perpendicular 12. A contactpoint 9, 1 0, will then travel at a changing rate along line 6 as hereafter explained. In other words,-the hob will have a changing lead whichhas been found to affordseveral advantages as later described.

The mesh between the pitch plane 2 gear andthe pitch cone 5 of t l tained when thesaid pitch (if no oi? the rate of the developed hob.

sine of the cone angle 16 ot the hob r igure 2). In this deve oped relation the crown gear and hob development mesh like two gears of pa allel i and 1-. lhere are accordingly two circl 1'7 and 18, which roll upon each other without sliding, which are ordinarily termed pitch lrcles and whose radii are in the inverse proportion of their respective angular velociti it is preferred to employ an internal mesh s shown, one circle 18 rolling intern l on the other circle 17, or, in other words, h the developed hob and croi n gear turning in the same direction of revolution. Moreover the ratio in development, Figure 3, is pre erably less than 5:1. tie crown gear turningfaster than As an er:- ample within theabove general ratio, the dimensions of the circles 17 and 18 of Figure 3 corresnond to a ratio of 1.8: 1.

The ratio between the :.:ctual he; and its development is determined in the same way as the ratio between a bevel gear and its crown gear; that is,- it corr sponds to the sine of the cone angle. Let (4 represent thecone angle 16' of the hob N the number of its starts, and let"(1 be the cone angle otthe bovelet gear blank and N its tooth numb The ratio between the hob and its development equals sin (a, and the ratio between tl blank and the crown equals sin c. follows T from what has been said, that the ratio l) between the blanl; and the actual hob is less than 5 sin a sin (t sin (t N sin a N It is well known in the art that in the case of a pair of gears of given-center distance and ratio, the line of action may be assumed and the mate tooth profilesim such line of action then determined. Thus, in Figure 3, line i has been assumed as the line of action. This i not the usual line of action for an actual pair oi? gearss-ince it passes through th e center e of one of the gears whereas ordinarily the line 'ota'ction p sscs through the contact point 19 of pitch circles 1'? and 18. Nevertheless, tie tooth profiles meshing alon the line of action 6 are subject to the cal requirements. The profile perpendicniars 2O, 21, at any pointsot contact 9, 10, 1211 pass through contact point 19. This relation gives the inclination of the profile tar nts for points at any distance trom the centers 1 and 4 and the tooth profiles themselves may also be readily determined. From the above comparison of the mesh between the pitch surfaces 2 and 5 with the mesh between the tooth profiles of a pair of gears of parallel axes, it w'll be understood that the term tooth profiles as used in the above explanation applies to the pitch lines oi hob and blank, that tudi-nal profiles off the tooth or thread.

it follows from the foregoing, therefore, that the pitch lines of a hob, or simply its thread spiral, should be such that perpendiculars to it at all the points oi the straight line 01" action 6 pass through a single point 19. T he setting oi. the hob is preferably such that the said point is situated in the line connecting the apices of the gear and hob 1 and l, respectively. a

In the development, Figure 3, the convex pitch lines of the hob apparently interfere with the concave pitch lines of the crown gear. That is, although contacting in a point of the line of actions, the pitch lines appear to cut into each other on either side of the point of contact, since the concave pitch lines of the crown gear have a sharper curvature than the convex pitch lines of the hob. Such an interference appears in development only and not in actuality, when the pitch lines 7 are wrapped on a hob of suitable diameter.

The general equation of the thread spiral also t s: E cos b an r+E sin?) where E equals the distance from the center a to the point 19 and b is the angle between line 22 and perpendicular 12. By substituting in the first of these equations the value is to the longi- 7 for tan 8 obtained in the second, simplifying and integrating, it is found that r r I I +tan I) log 1",

this being the general polar equation of hob spirals in development. It is preferred to use a hob thread which corresponds to E m (infinity) and the above equation then, assumes the simpler form tan b log r which is the equation of a logarithmic spiral. Giving to E the value infinitymeans that the pitch circles 17 and 18 contact at a point 19 at an infinite distance in extension of line 22. become equal, since they differ only in the finite distance between the centers 1 and 4. In other words, the ratio between the crown gear and. hob development is 1:1. The perpendiculars 20, 21 all become parallel toline 22 since they intersect the latter in the-point 19 as infinity. The lead angle 8 therefore becomes constant and it has been found that a thread of constant lead angle is of great advantage,-especially in the case of comparahob at 4 and the line of action at 6. It is to be noted that, as explained above, the perpendiculars 20, 21 are parallel to each other and to the line joining centers 1 and 4. The shaded areas represent sections through the teeth of the gear and hob, the sections being taken along the pitch surfaces. The gear here shown is a development of the gear to be cut, the characteristics ofwhich are best illustrated and disclosed in this manner.

Since the gear and hob match along the line of action 6, the pitch lines ofthe crown gear or of the bevel or other tapered gear in development have the same inclination as the pitch lines of the hob along this line. The pitch lines of the gear have therefore a constant inclination against line 6,01 any other line 25, lying at the same distance from the center 1. Thus, the inclination angle 26 of the pitch lines 27, 28, 29, is constant.

Figures .3 to 8 inclusive illustrate the generation of a pinion and mating gear. Fig: ures and 6 illustrate the generation of a bevel pinion 30, the pitch cone of which and of the hob 31 are placed in tangential'relation to a plane 32 representing the pitch plane of a crown gear 33, Figure o, having an.

The hob and pinion blank are roaxis 34. tated in continuous cutting engagement in timed relation about axes 35 and 36-, while an additional feeding motion between them is The radii of these pitch circles thus spiral of the flutes. mic spiral flutes such as illustrated in F1117 ure 9, hob 57 is moved at a rate proportional to the distanceof the grinding line '60 from imparted. aboutthe apex of the blank, or axis 7 34, as well understood in the art. Preferably such relative feeding motion isaccomplished by swinging the hob, but if desired such motion may be imparted to the blank instead or distributed between the hob and blank to accomplish this, feeding or generating roll, as well understood in the art. The hob is fed in the direction 37,'Figure'6, and is shown midway in its generating roll.

Figures '7 and 8 illustrate the generation of a mating gear 38 adapted to mesh with the pinion of Figures 5 and 6. The axes and 39 of hob 31. and 40, Figures 5 and 7, respectively, pass the axis 34 ofthe basic crown gear on opposite sides and hobs 31- and 40 are of opposite hand, as well understood in the art. Hob 40 is preferably fed in the direction of arrow 41 about'the axis 34 of the basic crown gear. v

Figure 9 shows the developed pitch cone of the hob with its threads cut by flutes or gashes to form the cutting teeth 51 appearing in section at the pitch lines. The gashes 50 extend as shown along curved lines and preferably along logarithmic spirals having the same inclination s at any radius 52, 53, 54, drawn from the apex 5 5 of the hob. Such gashes therefore are curved in actuality as well as in development. Since the thread of the hob also extends along logarithmic spirals and has therefore a constant spiral angle at any such radius 52, 53, 54, the angle between the thread and flute is constant for the whole length of the hob. This angle,

furthermore, may be made a right angle, as

shown in Figure 9, to thusinsure equaland efficient cutting on both sides of the tooth. The actual h ob is illustrated in Figure 12 and 'more particularly described hereafter;

The novel taper hob with its curved llutos may be readily ground as for example by the means and methods illustrated in Figures'lO and 11. The flutes 56 of such a hob 57 may thus be ground with a conical grinding wheel 58 swung to the spiral angle 8 k V The axis 09 of the grinding.

of the flutes. wheel s inclined with'respect to'the. plane of the paper in Figure 10 to present a grinding line 60 perpendicular to the paper. This line 60 is approximately theconta-ct line between i the grinding wheel and the face of a flute. Hob 57 when turned uniformly about its axis 61 is moved at a changing rate in the same direction as line 62 in accordance with the In'the case of logarith-.

the apex of the hob. 'A. successive position of the hob axis 61 is shown at 61, Figure 11. The motion of the hobis preferably guided flutes (36. A

insane? sit-ioned to engage body 63 along a line of the gear and both sides oi each tooth are corresponding the grinning line 60 and simultaneously shaped in one continuous corresponding in position on the master bed. It flutes 0t other than logarithnjnc spiral "form are provided, disk corre ondi the sha 3c of 'llllfillil wheel 58 should be used 1 instead or win his oat-cause ndcr sucn con- 1 i ditions wneel 58 will generally not grind along a iixed-grir ling line owing to the varying inclination of the flutes to the grinding wheel.

Figure 12 shows an actual hob .apted tor accomplishing the method 0' t invention. its cutting teeth 7G, Ti, .n, T l, F5, ar arranged as shown in multiple three Cutting edges 7e, 77, are termed on the teem by flutes 78, 79 of the ch raeter described, and it is to be ioted from Figures and flutes and the number of threads or starts preferably contain no common factor. Thus the hob shown in Fig ure 12 six threads and live flutes. lit has been found that hobs so constructed apply a smoother finish than wou d hob or": six threads and six flutes, for example. Furthermore, it is preferred, in bobbing a blank, to use a hob with a number ot threads having no factor in commonwith the number or teeth of blank. Thus, the six threaded hob may be advantageously used to cut a blank oi twenty-three or twenty-live teeth but it is preferred to use a di eerent hob for a blank of twenty-four teeth, since the latter nun ber contains as a factor the number of threads (six) of the hob. l seven threaded hob for instance would afford better results for a blank of twenty-tour teeth.

As shown in Figure 12, the cut-ting edges 76, 7?, re curved and convex and the teeth that the number or L Liu are relieved back of the cutting faces to af'ord cliicient cutting action. F1 gurcs 13 and 1% iliu trate two diiierent ways of applying rell to the teeth of a hob ot the character de scribed. In Figure 13 the dotted line 80 indicates the cutting edge after resharpcning of the original edge shown in lull line, tollowing one method of relieving. It will be seen that the new edge 80 is located inwardly of the original edge 82, receding in a direction 83 substantially at right angles to pitch line 81. In Figure 14, on the other hand there is shown a new edge 81 result" from relieving the original or if in a eirecti, 8'16. Either kind oi? relief may be app to the present hob. ln cutting and in ing the hob a suitali ly inclined tool is led along the pitch line 8?, Figure 12 at a rate of advance varying with relation to the rotation of the hob and controlled for example by suitable cams in place of the usual lead rapid and gears which conin selecting a taper nob ct changing lead. the sine of whose cone angle is in the same proportion to sine of the cone angle oi the blanks the number of its threads bears the number teeth on the to becut l in rotating the hob and blank in timed rention while imparting additional relative movement between the hob and blank about the apex of the latter.

The method of cutting ears adapted to mesh int rchangeably with a basic crown gear which consists in employing a hob oit changing lead so proportioned 1n developm rit relative to the crown gear that the ratio 0' angular velocities of the developed hob and crown gear is inversely proportional to the ratio of the distances of the respective apices from the intersection of the perpendiculars to the hob spirals at the line oi action, and in rotating the hob and blank in timed relation while imparting an additional rclati ve inoven'ient between the hob and blank about the apex of the latter.

The method of cutting gears consisting in selecting a hob having a thread the perpendicular-s to the pitch line of which the intersections thereof with a generatrix of the pitch surface of the hob, intersect in a joint, positioning the hob with respect to a blank so that the hob apex, the blank apex and the said point of intersection lie in a straight line intersecting the axis of the hob at an acute angle, and rotatin the hob and blank in timed relation while imparti: g an additional relative movement between the hob and blank about the apex of the latter.

4t. The method of cuttii'ig curved tooth bevel gears adapted to mesh interchangeably with a basic crown gear having teeth of con' stant lead angle along a St-l'fll l line o 'set from its apex, consisting in selecting a j adapted to mesh with the crown geai such a line and rotating the hob and o unk in timed relation while in'iparting an additional relative movementbetwcci them about the apex ot' the blank.

5. The method of cutting curved tooth bevel gears consisting in positioning a hob so that aline perpendicular to the hob thread at the intersection thereof with a generatrii: of the pitch surface of the hob is iarailel to a line connecting the hob and blani; apices and rotating the hob and blankin t-imed relation while imparting an additional relative movement between them about the apex of the blanln 6. The method of cutting gears consisting in employing a hob of changing lead whose pitch lines in development have a constant inclination to the line of action between the hob and blank to be cut and the same inclination as the pitch lines of the latter and in rotating the hob and blank iii timed relation while imparting to them an additional relative movement about the apex of the blank. i v

7. The method of cutting gears adapted to mesh interchangeably with a basic crown gear consisting'in employing a tapered hob of constant lead angle adaptedto mesh with the crown gear along a line of action passing through the apex of the hob and in rotating the hob and blank in timed relation while imparting to them an additional relative move mentabout the apex of the blank in the man nerol' a gear meshing with said basic crown gear.

8. Themethod of hobbing bevel gears consisting in positioning a. hob so that a perpendicular to its thread at tne intersection thereof with the generat 'ix of its pitch surface is parallel to a line connecting the hob and blank apices and in rotating-the hob and blank in timed relation while imparting to them an additionalrelative movement about the apex of the blank.

9. The method of bobbing bevel gears having teeth of changing spiral angle consisting in employing a hob of constant spiral angle and in rotating theliob and blank in timed relation while imparting to them an additional relative movement about the apex of the blank.

10. The method of cutting curved tooth bevel gears consisting in rotating a taper hob of changing lead in cutting engagement with a blank while imparting an additional relative movement between the hob and blank about the apex of the latter.

11. The method of cutting curved tooth bevel gears adapted to mesh interchangeably with a basic crown gear consisting in employing a hob having in development the same angular velocity as the basic crown gear and rotating the hob and blank in timed relation thread taper hob, the number of threads and cone angle of which bear a predetermined mathematical relation to the tooth number and cone angle of the gear to be cut, and in rotating the hob and blank in timec relation while imparting to them an additional relative movement about'the apex of the blank.

14. The method of cuttinggearsconsisting in rotating hob of constant lead angle in continuous cutting engagement with a rotating blank while imparting an additional relative movement between thehob and blank about the apex 'ot' the latter.

15. Themethod of cutting gears consist? ing inrotating a taper hob of constant lead bevel gears consisting in selecting a multiple angle in continuous cutting engagement with a rotating blank while imparting an additional relative movement betweenthe hob and blank about the apex of the latter.

16. The method of cutting gears consisting in positioning a taper-hob of constant lead angle representing a basic crowngear 'ot the system, relative to. the blank-to be cut, so that the pitch surfaces of hob andblank mesh along a line which passes throughthe apex of the hob and in rotating the hob and blank in timed relation while imparting an additional relative movement between them about the apex of the blank and maintaining the apex ot'thehob outside a perpendicular basic crown gearto.

from the centerof said the hob axis r 17. The method of cutting gearsconsisting inrotating a taper hob of constant lead angle in cutting engagement with a rotating blank while imparting to them an additional relative movement about the apex oftheblank, and maintaining the hob apex in predetermined offset relation to the apex of theblank.

18. The method of cutting gears adapted to mesh interchangeably with a basic crown gear consisting in rotating a taper hob and blank in timed relation and imparting to them an additional relative movement about the apex of the blank while maintaining the angle between a line connecting the apices of the hob and blank and the projected hob axis equal to the lead angle of the'hob. v

c 19. The method of cutting gears adapted to mesh interchangeably with a basiccrown gear consisting in employing a taper hob of changing lead whose pitch surfacesrmatch those ofthe basic gear along a line passing through the apex of the hob and inv rotating the hob' and blank to be cut in timed relation while imparting to them an additional relative movement about the blank apex.

20. The method of cuttinggears adapted to mesh interchangeaby with a basic crown gear consisting in rotating a taper hob and blank in timed relation and imparting to them an additional relative movement about the apex of'the blank while maintaining the apex of the hob outside a line drawn from the center of said basic crown gear perpendicular to the projection of the hob axis.

21. The method of cutting gears adapted to mesh interchangeably with a basic crown gear consisting in employing a hob adapted in development to mesh with the basic gear with a ratio less than 5 to l and in rotating the hob and blank to be cut in timed relation while imparting to them an additional relative movement about the blank apex.

22. The methodof cutting gears consisting in employing a tap-er hob having a cone angle determined in accordance with the formula an N where 11 and a are the cone angles of the hob and blank, respectively, and N and N their respective tooth numbers.

23. The method of cutting gears consisting in employing a taper bob the number of whose threads contains no factor in common with the-number of teeth to be cut in the blank.

24. The method of cutting gears dapt-ed to mesh interchangeably with a basic crown gear consisting in rotating a hob in contin uous cutting engagementwith a blank while imparting an additional relative movement between the hob andblank about the axis of the blank and maintaining the hob so positioned with respect to the basic gear axis that perpendiculars to the thread of the hob inter-- sect at a point which lies outside of a line drawn from the basic gear center perpendicular to the hob axis.

25. The method of cutting gears consisting in selecting a hob, the perpendiculars to whose thread at the intersections thereof with a generatrix of its pitch surface intersect at a point, and in positioning the hob so that the said point of intersection and the apex of the blank lie at opposite sides of the hob axis in a line intersecting the latter at an acute angle.

26. The method of cutting curved tooth tapered gears which consists in rotating a taper hob of constant lead angle in engagement with a tapered gear blank, while imparting a relative movement between the hob and blank in the manner of a gear meshing with a crown gear to generate the tooth profiles.

27. The method of cutting a curved tooth tapered gear which consists in positioning a taper hob of constant lead angte with its axis offset from the axis of the blank and eX- tending diagonally across the face of th blank and rotating the hob in continuous cutting engagement with the blank while imparting a relative movement between the hob and blank in the manner of agear meshing with a crown gear to generate the tooth profiles.

ERNEST NILDH'ABER. 

